I understand the concept, but how would it have been suspended during construction? That would be my first question.
scaffolds...............
There are YouTube videos of folks making the bridge in their backyard.
“I understand the concept, but how would it have been suspended during construction? That would be my first question.”
I imagine a temporary wooden framework underneath would support the masonry. Once the keystone is set, the wood would be removed. That’s the way a kid’s project at a science museum that I went to worked.
What you do is, you dry up the river by diverting it (let someone else worry about that part). Then you pile up a bunch of compacted sand and rocks, then you build the bridge over the compacted sand and rocks, then you un-divert the river (the same guy who diverted it can do this) and allow the river to wash away the compacted sand and rocks which you helped by boring holes through the sides of the pile. Easy-peasy...
It looks like Da Vinci was leveraging well establish Roman building techniques by leveraging the arch along more than one axis. Heck a dome is just an arch rotated about its central axis.
If this bridge were to be over a river I would expect that the Romans would simply divert the river, construct as scaffold, build their arch bridge, then allow the river to resume it’s previous course. Brute force IOW’s.